The present invention relates to a housing for a temperature sensor assembly used in a thermometer where the housing material and the sensing element assembly material have different coefficients of thermal expansion. The sensing assembly includes a mandrel having an element section supported in a bore in the housing with an electrically insulating, compliant potting material, comprised of loose powder, while a support section of the mandrel is held in place with a rigid potting material at an outer end of the bore. The powder provides a necessary cushion and limits displacement of the temperature sensing element during vibration and mechanical and thermal shock, while the mandrel support section is held securely in place with the rigid potting material.
Resistance temperature thermometers are well known, and in many applications they are made with a platinum resistance wire element wound onto the sensing element section of a mandrel. The resistance element can be a thin wire, or a thin film, with the mandrel supported in a suitable heat conducting housing, and potted in place in a bore in the housing. The housings are generally aluminum, aluminum alloys, stainless steel or other heat conducting material with a high coefficient of thermal expansion, and the mandrels are generally made of a material that has a much lower coefficient of thermal expansion. The potting material also has a different coefficient of thermal expansion from the other materials. When using a wire wound thermometer the wire is wound on the outer surface of the mandrel, and may be protected from the elements with a thin layer of glass. Expansion and contraction of the surrounding housing material has a significant effect on the thermometer performance. The differences in the coefficient of thermal expansion between the housing material, the core or mandrel material, and the potting material, create internal stresses and strains on the wire element as the environmental temperature changes.
In normal use, such as in space vehicle applications, the temperature sensor will be subjected to cryogenic temperatures as well as high heat, so that there is a significant range of sensed temperatures that will cause stresses due to the differences in coefficient of thermal expansion. The support for the sensing element has to be capable of withstanding high vibration and shock loads without damage, and without affecting the sensor accuracy.